This invention relates to films containing lyotropic polybenzazole ("PBZ") polymers and processes for drying and heat-treating them.
Processes to dry and heat-treat PBZ film have depended upon the film being constrained in both the machine direction and the transverse direction in order to prevent undesirable side effects such as shrinkage and wrinkling. There is mention of the need for constraining the film during the drying process on page 268 of the article, "Film Processing and Applications for Rigid-Rod Polymers," by Lusignea, The Materials Science and Engineering of Rigid-Rod Polymers, Mat. Res. Soc. Symp. Proc., Vol. 134, pp. 265-276, .COPYRGT.1989 by Materials Research Society, as follows "Drying of the water-soaked films results in a reduction in thickness to 1/5 the thickness of the wet film. For this reason, dimensional constraints are needed during drying to control the stress in the film."
Constraint of film in the transverse directions during drying (and heat-treating) is an expensive process because it requires special equipment. It is desirable to have a process for drying and heat-treating polybenzazole films which requires constraint of the film in only the machine direction.